Transport mechanism for disk-shaped workpieces

ABSTRACT

A transport mechanism for disk-shaped workpieces has a horizontally movable transport arm with two elongated carrying elements at one end, for receiving the workpiece. A cassette which includes a comb structure at each side for receiving several workpieces, is inserted free of contact between two adjacent combs with workpieces therein for vertically lifting a workpiece. The carrying elements are disposed such that during a cassette engagement they are each positioned substantially adjacent and parallel to the comb structure along a comb, and that in this region along and between two adjacent comb planes on one side of the cassette, a scanning beam is provided for workpiece acquisition, and that the scanning beam is relatively height-positionable with respect to the cassette. The scanning beam is tilted about a small angle with respect to the horizontal workpiece plane.

FIELD AND BACKGROUND OF THE INVENTION

The invention relates to a transport mechanism for disk-shapedworkpieces, in particular for semiconductor wafers.

In modern vacuum process facilities circular flat substrates orworkpieces, which are also referred to as wafers, are surface treated,such as for example coated, etched, cleaned, thermally treated etc., insuch fully automated vacuum process systems. In order to automate suchprocesses and to be able to carry out multi-stage processes in differentfacility areas, automated transport systems, a type of handling robot,are employed. In particular the treatment of semiconductor wafers insuch processes requires very high quality of treatment, such as inparticular high cleanliness, high precision and careful treatment of thesubstrates. Due to the stated high requirements, such facilitiespreferably include a lock chamber, where the wafers are moved from theatmospheric environment into a vacuum chamber and subsequently into aprocess station or, as a rule, sequentially into several processstations in order to be able to carry out the required surfacetreatment. With the aid of a transport device the wafers are deliveredin a horizontal transport plane from the lock chamber into the processchamber, and after the wafer has been deposited in the process chamber,the latter is, as a rule, closed in order to be able to carry out theprocess under the required vacuum and process conditions. If severalprocess steps are necessary, the wafer is again transported out of theone process chamber in the same manner and, for the next process step,is transported into another process chamber. Especially preferred typesof facilities are so-called cluster systems. In such systems, the lockchamber and the process chamber, or the several chambers, are arrangedperipherally about the substantially central transport chamber. In thecase of more than one lock chamber and in particular in the case ofseveral process chambers, these chambers are arranged in a type ofstar-shaped configuration about the centrally located transportchambers. The transport device in this case is located in this centrallylocated transport chamber and has access, on the one hand, to the atleast one lock chamber and, on the other hand, to the process chamber.Between the transport chamber and the remaining chambers conventionallyand preferably a so-called lock valve is disposed in order to be able topartition the chambers against one another during the locking process orduring the process step. During the transport process of a wafer, thetransport device subsequently extends appropriately through the openlock gates in order to deposit the wafer at the designated location.

The transport device moves the wafer translatively in one plane andconsequently in two directions of motion. In said preferred clustersystems with the transport device disposed in the central transportchamber, the device is conventionally formed as a mechanism which pivotsabout a center of rotation and forms therewith the one rotatingdirection of motion and which can execute a further second translatorymotion radially with respect to the center of rotation back and forthaway from/to this center of rotation. On this transport device, forexample a length-adjustable arm mechanics rotatable in the horizontalplane, the wafer to be transported is subsequently deposited in the endregion of this arm. Such a configuration can in this case readily alsotransport a wafer over relatively great path distances, for example ofthe orders of magnitude of 1 m or more, from a lock chamber into thetransport chamber and from here, in turn, into and out of the processchamber and extend through the corresponding opened lock doors. At thebeginning of the transport cycle the wafer is deposited underatmospheric pressure onto the transport mechanism as precisely aspossible and always in the same position in order to be able totransport it subsequently also precisely to a predetermined position.However, the deposition of the wafer on the transport mechanism, as wellas also the transport mechanism itself, is afflicted with imprecisionsor with tolerance errors. Further imprecisions or shifts of the waferposition on the transport mechanism can also occur in the processstation due to effects in the process chamber.

A particular problem in the handling of disk-shaped workpieces occurs ifthe workpieces are very thin relative to the diameter and deflectcorrespondingly strongly. This is in particular the case withsemiconductor wafers, which have perhaps a thickness of a few tenths ofa millimeter, such as preferably 0.07 to 0.3 mm at a diameter of 100 mmto 300 mm. Depending on the type of support the deflection may be in therange on a few tenths of a millimeter up to a few millimeters. Thismakes precise handling and positioning within a transport configurationconsiderably more difficult especially since the deflection can be ofdifferent magnitudes. Especially problematic is the handling or transferof semiconductor disks from a cassette into the designated positions,such as process stations or chambers of a vacuum process facility. Insuch facilities the semiconductor wafers are deposited horizontally inmagazines formed as cassettes and again removed horizontally from them,in order to intermediately store them on compact space. Specialdifficulties are encountered with wafers which deflect strongly, withrespect to handling precision and desired compactness of theconfiguration and reliability of the handling.

EP 0 696 242 B2 discloses a transport mechanism for semiconductor waferswhich permits lifting and depositing circular semiconductor disks, ordisk-shaped workpieces, with the aid of a height-adjustable handlingrobot rotating about its axis with a carrying arm or carrying elementextensible in the horizontal plane or to deposit them and bringing theminto a different position. Therewith it is possible for example toremove workpieces with a transport arm from a cassette and transportthem into a different position, where they can, for example, be worked.In vacuum process facilities the workpieces must be moved in and outthrough a lock, be that from atmospheric pressure into the facility orwithin the facility between different chambers. The previously describedtransport arm of the robot, if needed and under control, reaches throughthe corresponding lock gates for the transportation of the workpiece tothe correct target location. Depending on the concept of the facility,for the intermediate storage of the workpieces cassettes are utilizedwhich can hold several workpieces in a small space and can be employedeither outside of the facility and/or inside the facility. Thearrangement introduced in the patent permits realizing transportmechanisms of this type. The underlying assumption in these knowntransport mechanisms is that the workpiece remains flat as defined andthat its dimensions are also defined. The handling as well as also thesubstrate acquisition with the appropriate electronic or optical sensorsbuild on these prerequisites.

However, for large-area thin workpieces, which deflect strongly,considerable problems are encountered with this mechanism and a solutionof them is not provided. In these cases such transport mechanisms arecorrespondingly functionally also operated at their limit, whichdecreases the operational reliability of such facilities.

SUMMARY OF THE INVENTION

The present invention addresses the task of eliminating the previouslylisted disadvantages of prior-art. The task consists in particular inrealizing a mechanism and a method for the transport of thin flexibledisk-shaped workpieces, in particular of semiconductor disks, whichpermit high precision and reliability, in particular as much as possiblewithout workpiece defects, with which high economy in the productionprocess can be attained.

According to the invention the task is solved through a transportmechanism for workpieces according to the invention and with a methodaccording to the invention. The claim define the various advantageousembodiments of the invention.

According to the invention the solution is comprised by permitting thedeflection of the flat workpiece up to the natural form and the handlingand detecting takes this deformation of the workpiece into considerationand is referenced and oriented to positions or places which are clearlydefined at the beginning of the transport process and are maintainedduring the entire process. All handling and detection elements arefocused under consideration of the tolerance ranges and their limitswhich are given mechanically and electrically through the participatingmechanism in the process facility referenced to the starting position ofthe workpiece in the process facility. The process facility is sorealized that none of the regions not located within these clearlydefined zones can have a significant effect on the function or thereliability of the transport or handling process.

The invention comprises a transport mechanism for disk-shapedworkpieces, in particular for semiconductor wafers, with a controlled,horizontally movable transport arm at the one end of which two elongatedcarrying elements are disposed at a spacing for the substantiallyhorizontal reception of the workpiece and that a cassette is providedwhich at two opposing sides has a comb structure for the substantiallyhorizontal reception of several workpieces, the carrying elements andthe comb structure being formed such that they can be introduced free ofcontact between two adjacent spaced-apart combs of the comb structurewith the workpieces potentially disposed therein for the lifting ordeposition of a workpiece with the aid of an additional vertical motionrelative with respect to the cassette and the transport arm, thecarrying elements being disposed such that during the cassetteengagement they are substantially each positioned adjacent parallel tothe comb structure along a comb and that in this region along andbetween two adjacent comb planes on one side and/or both sides of thecassette a scanning beam is provided for acquiring a workpiece and itsposition, and that the scanning beam can be height-positioned relativelywith respect to the cassette, the scanning beam with respect tohorizontal workpiece plane being guided at a small-angle tilt.

The various features of novelty which characterize the invention arepointed out with particularity in the claims annexed to and forming apart of this disclosure and are entirely bases on the priorityapplication no. 2005 01843/05 filed in Switzerland on Nov. 17, 2005,incorporated here by reference. For a better understanding of theinvention, its operating advantages and specific objects attained by itsuses, reference is made to the accompanying drawings and descriptivematter in which a preferred embodiment of the invention is illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be explained in further detail byexample and in conjunction with schematic figures. In the drawingdepict:

FIG. 1 a disk-shaped workpiece, such as a semiconductor wafer, in topview and in different cross sections with different examples ofdeflection,

FIG. 2 a a workpiece in the region of the support with the maximallypossible deflections,

FIG. 2 b a workpiece in top view with defined possible support regions,the handling zones,

FIG. 3 a a cassette in cross section with several workpieces depositedtherein and partially bent,

FIG. 3 b a cassette in top view with a workpiece,

FIG. 4 a a cassette in cross section corresponding to FIG. 3 a,

FIG. 4 b a detail of the cassette with comb structure on one side with aworkpiece in the region of the support,

FIG. 4 c a workpiece in top view with the resulting permissible handlingzones,

FIG. 5 a workpiece in top view with demonstration of the support on thecarrying elements which are overlaid within the permissible handlingzones,

FIG. 6 a a workpiece in cross section with demonstration of the scanningbeams along the comb structure,

FIG. 6 b in cross section workpieces deposited in the cassette withdifferent possible deflections,

FIG. 6 c a detail according to FIG. 6 b on one side of the cassette inthe region of the support and in cross section with respect to thescanning beam,

FIG. 6 d in top view a workpiece in the cassette with demonstration ofthe imaging zones of the scanning beam on the workpiece,

FIG. 7 a in cross section a bent workpiece with support on posts,

FIG. 7 b in top view a workpiece according to FIG. 7 a with carryingelements guided under the workpiece,

FIG. 8 a in cross section workpieces deposited in a cassette which arebent with a warp,

FIG. 8 b in cross section a detail in the proximity of the combstructure of the cassette according to FIG. 8 a,

FIG. 8 c in top view a workpiece with warp deposited on carryingelements,

FIG. 8 d in cross section a workpiece with warp with formed carryingelement;

FIG. 9 a in top view a carrier plate for workpieces with radiallydisposed carrying elements,

FIG. 9 b in top view a further carrier plate for workpieces withcircularly disposed carrying element,

FIG. 10 a in top view a transport device with two transport robots,

FIG. 10 b in top view a configuration for the orientation of workpieces.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In fully automated vacuum process facilities for the surface working ofdisk-shaped workpieces and in particular of semiconductor wafers ofsilicon and/or germanium it is necessary to transport these preciselywith robot devices. The transport of these workpieces from one positioninto the other position must take place such that it is preciselyreproducible and without causing damage to the workpiece. Severalworkpieces 7 are for this purpose deposited into a cassette 20 orremoved from it, in order to be transported for example from atmosphericpressure into a vacuum through a lock, in order to be subsequentlyworked. After the working in a process station, for example aftercoating or etching of the workpiece, these are again guided back withthe aid of the handling robot through the lock into the cassette. Vacuumprocess facilities may also comprise several process stations, which aretended with one or several handling robots. In such process facilitiesthe flat disk-shaped workpieces 7 are conventionally transported in thehorizontal direction. For this purpose are employed handling robots,which can be rotated about their own axes 66, 67 and which have atransport arm 61, 60 which can be extended in the horizontal directionlaterally to the rotational axis 66, 67, in order to be able totransport a workpiece 7 in the lateral direction to these axes, such asis schematically shown in FIG. 10 a in top view. The receiving ordepositing of the workpiece takes place thereby that the carryingelements 26, 27 are moved under the workpiece 7 and subsequently islifted or deposited with a vertical relative motion from the cassette 20or a base 62, 42, 54 through relative movement. The relative movement isgenerated thereby that either the cassette or the base iscorrespondingly moved vertically or preferably the handling robot ismoved correspondingly vertically. These processes must be carried outhighly precisely and no grinding or frictional movements must begenerated at the participating elements, which would lead to undesirableabrasion and particle formation, which would unfavorably affect thesensitive vacuum processes and would lead to rejects in the production.The situation is additionally made difficult if thin large-areadisk-shaped workpieces 7 are to be worked and must be transported sincesuch workpieces can have a strong deflection or warp and may therebyimpair the reliable function of the transport mechanism. To increase theeconomy in the semiconductor production further, increasingly greaterdiameters of workpiece disks are utilized today and these areadditionally increasingly becoming thinner, whereby the bending problemis exacerbated. Today disk diameters of 100 mm to 300 mm are utilizedhaving thicknesses of 0.07 mm to approximately 0.6 mm. Depending on theratio, deflections result therefrom which are in the range of a fewtenths millimeter or may even go up to several millimeters.

For the support of workpieces 7 two line-form supports 1, which form thecarrying elements 26, 27 are preferably provided, as is shownschematically in FIG. 1. The line-form supports 1 are substantiallyaligned parallel to one another and spaced apart from one another suchthat the disk-shaped workpiece 7 is stayed in the margin region on bothsides along the support line 6 on the supports 1. These two supports 1are preferably formed as rod-shaped carrying elements 26, 27. FIG. 1shows as the workpiece a semiconductor wafer with different types ofpossible deflections. A relatively thick wafer 2 has essentially nodeflection and rests flat on the supports 1. Thin wafers can deflectdownwardly 3 due to their own weight or upwardly 4 due to internalstress. These deflections conventionally have cylindrical form, however,they may also be formed of a combination of several cylindrical forms,which are oriented differently. This combination of deflectionssubsequently leads to a deflection profile 5, which has a saddle-shapedwarping of the wafer. In standard vacuum process facilities for workingsemiconductor disks, these are introduced in cassettes containingseveral wafers. In such cassettes 20 the wafers rest with their marginregion in contact on stays guided in parallel, such that the surface ofthe workpiece is substantially free. Only the zone of the wafer in theregion of the stayed region is hereby well defined in the verticalposition independently of the magnitude of the deflection of theworkpiece. This position can be characterized through two support lines6, which form two chords in the region of the periphery of the wafer 7.Locations on the wafer face too far removed from these support lines 6,are not known or not defined in their vertical position.

In order to define an area about the support lines 6 which can beutilized for the handling, thus for the staying and detecting of thewafer, the system tolerance region 8 in the vertical direction isdeterminant, as is shown in FIG. 2 a in cross section. If the maximallypossible deflections upwardly 9 and downwardly 10 of the workpiece aretaken into consideration, an angle deviating from the horizontalresults, the upward angle 9 and the downward angle 10 with respect tosupport 1, from which subsequently the maximum handling zone width 11can be defined, which define the handling zones 12, 13 on the workpieceon both sides. Thus, virtually two spaced-apart, parallel strip-shapedhandling zones 12, 13 result, which are located in the peripheral regionof the disk-shaped workpiece, as is depicted in top view in FIG. 2 b.

If the rules as they were previously defined are applied to a cassette20 for thin workpieces 7, it is evident that the support zones of theworkpiece 7 are limited to two parallel zones 12, 13 in the proximity ofthe periphery of the workpiece 7, as is shown in FIG. 3 a in crosssection and in top view in FIG. 3 b. In conventional wafer cassettes 20according to the SEMI standard, on each side of the workpiece oneadditional end support means 14, 15 is disposed which projects into theinterior region of the cassette 20. Such inwardly projecting supportmeans 14, 15, shown in dashed lines in FIG. 3 b, cannot be utilized inthe present invention. In order to limit or to define the horizontalposition of the workpiece 7 in the cassette, stop means 16, 17 must beprovided which only occupy as spots the interior region of the cassettebetween the supports 18, 18′ or permit in the region of the supports andthe handling zones 12, 13 the detection means to extend between andalong them. Thin rod-shaped elements 16, 7 are therefore preferred asthe stop means. The cassette 20 has a comb-shaped structure 18, 18′ onboth sides, which forms a slot-form configuration capable of receivingand staying the disk-shaped workpieces 7 in the peripheral region. Thecassette 20 thereby forms a configuration with several receiving slotsfor the reception of several workpieces 7. It is important that the combstructure has a comb distance 19 large enough to avoid that adjacentlyinserted workpieces 7 do not come into contact even in the presence ofdeflections. If, for example, workpieces 3 are utilized which benddownwardly and workpieces 2 which are flat, the comb distance 19 must begreater than the downwardly directed deflection 3 of the workpiece 7. Ifworkpieces 7 are utilized, which deflect upwardly as well as downwardly,the comb distance 19 must be greater than the sum of the maximallyexpected bending upwardly and downwardly.

To be able to lift and carry the workpiece 7, carrying elements 21, 22are located at the end of the robot carrying arm, onto which theworkpiece 7 is deposited. On the horizontally movable carrying arm ofthe robot a carrying element mounting 28 is disposed and on thismounting two elongated spaced-apart carrying elements 26, 27 aredisposed in parallel, which are preferably formed in the shape of rods,as is depicted in FIG. 5 in top view. FIG. 5 shows the manner in which adisk-shaped workpiece, a semiconductor wafer 7, is deposited on thecarrying elements 26, 27. The thickness of the carrying elements 26, 27is limited, this means they must be sufficiently thin such that these[verb missing: provide separation(?)] between two adjacent workpieces 7in the cassette without touching it for the succeeding lifting processor after the deposition of a workpiece 7 in the cassette. The carryingelements 26, 27 are therefore preferably implemented in the form of rodsand must have sufficient rigidity in order not be bent in an undesirablemanner which would additionally increase the handling tolerances.

During the lifting and transporting of workpiece 7 the carrying elements26, 27 are directly in contact on the underside of the disk-shapedworkpiece 7. Around each of the carrying elements 26, 27 subsequently apermissible strip-shaped handling zone 24, 25 is defined, within whichthe carrying elements 26, 27 must move during the handling. Thedimensioning of the carrying elements 26, 27 is determined by the opendimensions in the loaded cassette 20. FIG. 4 a depicts by example awafer 3 in a cassette 20, which is bent downwardly compared to a flatwafer 2, both located in slots of the cassette,. The downwardly bentwafer 3 is to be lifted and removed from the cassette slot with thecarrying elements 26, 27. The maximally permissible thickness 21 of thecarrying element 26, 27 is a function of the available interspacebetween the superjacent and subjacent wafers 3, 2 and the handlingtolerances required to move the wafer into the cassette or out of it, asis shown in cross section in FIG. 4 b in detail in the critical marginregion. In the region proximal to the comb the greatest possibledistance between the adjacent wafers 2, 3 corresponds substantially tothe comb distance 19, whose position forms the outer position of thepermissible handling zone width 23 and the inner limit of thepermissible handling zone width 23 is spaced somewhat further away fromthe comb structure 18 toward the inside, which is limited by thediameter 21 of the carrying element 26, 27 and depends on thedeflections of the wafers 2, 3, without coming into mutual contact. Fromthese two possible positions results the permissible handling zone width23, which determine the permissible handling zones 24, 25, and must liewithin the handling zone 12, 13, as is depicted in FIG. 4 b and 4 c.

The definitions for the implementation of the cassette imaging systemwill be explained in the following in conjunction with FIG. 6 a to 6 d.Known imaging systems utilize for example reflecting laser systems, inwhich the read sensor 29 and the reflector 30 are disposed parallel tothe wafer surface and oppositely outside of the wafer. The read sensor29 is also the source of the laser scanning beam 31, which extends alsoparallel to the wafer surface and is reflected in the reflector 30 backonto the read sensor 29. This beam arrangement with scanning beam 31,read sensor 29 and reflector 30 is guided in known manner close to theregion of the center line of the wafer plane. If a wafer is moved intothe region of the scanning beam 31, the latter is interrupted and theposition is detected. This known method is utilized with relativelythick workpieces or semiconductor wafers which are thicker than 0.6 mm.Problems are encountered with thinner wafers if this method is utilizedfor the detection. If the wafer is thinner than the diameter of thescanning beam 31, yet is still flat, the scanning beam 31 is notinterrupted by the wafer 2. If the imaging system is to detect a loadedor an unloaded slot of the cassette 20, it is not possible to detectthis reliably with this method, since the center region of the wafer 2on which detection takes place, may belong, on the one hand, to a waferbent upwardly 4 or one bent downwardly 3, as is schematically shown incross section in FIG. 6 a, 6 b and 6 c.

To solve the first problem, according to the invention the read sensor32 and the associated reflector 33 for thin wafers is to be disposedoppositely outside of the plane of the wafer 2, 3, 4 and the read sensor32 and the reflector 33 is additionally to be disposed somewhat offsetoutside of the wafer plane, such that the scanning beam 35 is guidedslightly tilted with respect to the planar wafer plane 2, from which apreferred tilt angle 34 in the range of 0.50 to 2.00 results.

The small tilt angle 34 of the scanning beam 35 generates a projectionof the wafer in the direction of the scanning beam 35 such that asignificantly greater thickness 36, the so-called apparent thickness 36,seems present than the involved wafer, in fact, has.

The scanning beam 35 for thin bendable wafers 2, 3, 4 with the readsensor 32 and the reflector 33 are disposed in the margin region of thewafer periphery, thus in the proximity of the comb structure 18, 18′ ofcassette 20. Consequently, with a viewing direction in the scanning beamdirection not a dot-form beam appears as is conventional in knownsystems, but rather an apparent thickness 36 of wafer 2, 3, 4 dependingon the magnitude of the scanning beam tilt angle 34 as is depicted indetail in cross section in FIG. 6 c. The scanning beam 34 consequentlyhas the capability of acquiring, apart from planar wafers 2, alsocorresponding upwardly or downwardly deflected wafers 3, 4, whereby thesecond problem can also be solved. In order to be able to determine thesecond problem unambiguously, it is necessary to take into considerationthat close to the proximity of the comb structure 18, 18′ of cassette20, where the scanning beam 35 is guided, the vertical distance dbetween an upwardly bent wafer 4 and a downwardly bent wafer 37 withinthe same slot configuration is less than the apparent thickness 36 whichthe tilted scanning beam 35 provides. With the present, known, maximallypossible bending degrees of the wafers 3, 4 upwardly and downwardly itis possible to determine the maximum imaging zone width 38. The onelimit results through the tips of the comb structure 18, 18′ at which anupwardly bent wafer 4 and a downwardly bent wafer 3 were to intersect ifthese wafers 3, 4 were to lie in an adjacent slot of the comb structure18, 18′. Consequently two conditions must be maintained in order to beable to detect reliably thin bendable wafers. Firstly, as stated, theapparent thickness 36 in the region of the tilted scanning beam 35 mustbe greater than the maximally possible distance d in the laser beamregion from an upwardly bent wafer 4 and between a downwardly bent wafer3, if these were to lie in the same slot of cassette 20. As a secondcondition must be fulfilled that the actual determined handling zonewidth 39 for the measuring system lies within the maximal imaging zonewidth 38. From the handling zone width 39, thus determined, result thetwo imaging zones 40, 41, which are located on both sides of the wafernear the comb structures 18, 18′ of cassette 20, within which thescanning beam 35 can be guided and with the read sensor 32 and reflector33 located outside of the line. In this way within the imaging zone 40,41 every deformed thin wafer at any location within these zones can bereliably detected.

The handling of the wafer is conventionally so carried out that it ispositioned and deposited on a flat surface 42 before it is worked in theprocess station, as is shown in cross section in FIG. 7 a. To enable thesystem to correctly deposit the wafer on the surface, the originalsupport position is generated as in the cassette with supports, whichare referred to the handling zones 12, 13 on the wafer. For thegeneration or maintenance are utilized for example wafer support posts54, also referred to as pins, on which the wafer 3 rests and whichensure that the distance between base 42 and wafer 3 is large enough toallow carrying elements 26, 27 to be introduced between them as is shownin FIG. 7 a and 7 b. The wafer support posts 54 for this procedure arepreferably raised, whereby the wafer 3 is lifted from the base 42 and,if it is appropriately thin, is also deflected. To attain the lifting ofwafer 3 the wafer base 42 can also be moved in the vertical directionand holding elements other than the so-called wafer support posts 54 canalso be utilized for generating the distance between wafer and base 42.In the retracted state of the carrying arms 26, 27, for lifting ordepositing the wafer 3 on the base, the latter lies exclusively incontact in the region of the defined handling zones 12, 13 for thetransport procedure, with these arms being held on the carrying elementmounting 28, which is secured on the robot arm as is shown in FIG. 7 bin conjunction with an example of a semiconductor wafer 7.

Not all wafers are bent along a cylinder axis parallel to the handlingzones which are defined by the system. In the least favorable casewafers in a cassette can also be bent such that they are bent parallelto a cylinder perpendicularly to the support line. If such wafers arebent downwardly 44 or upwardly 43 and are placed in a cassette 20, theactual projection and definition of the form is not very different fromthose described previously. The determination of the cross section 45 ofthe carrying element 26, 27 and also the other sizes appear identicaland do not lead to a different configuration of the system. Carryingelements 26, 27 as depicted, using the carrying element 47 as anexample, in cross section in FIG. 8 d, can also be implemented formed,in order to adapt themselves to the bent wafer 46. In the presentexample each of the carrying elements 47 is provided with one step 48 inthe peripheral region of wafer 46 such that the wafer 46 can deflectdownwardly in the central region and thereby can adapt to apredetermined desired form, preferably to a planar surface in order tobe able to accept essentially the previously made considerationsdirectly. In the margin region further steps can preferably be providedin order to be able to secure the wafer there on the carrying element 47in order to avoid during the transport that the wafer becomes displacedduring the transport movement. It is also of advantage to fabricate thecarrying element 47 of a material or to coat it with a correspondingmaterial such that a greater surface friction results to decrease thepreviously described effect.

In a wafer process facility the sole location where the wafer carryingline method is not utilized is the wafer rotation orientation stationwhere wafers are oriented in their planar orientation with respect to aworkpiece marker 7 a. A wafer which has reached this station isconventionally by definition not oriented to the corresponding marker 7a. This means that the support axes are randomly oriented with respectto the wafer marker 7 a. The purpose of this station is to bring thewafer into a clearly defined rotation position in order to work itfurther. This means that the wafer must be rotated. This rotationmovement also leads to a rotation of the support lines about the centerof the wafer, which means the support lines before and after theorientation are different. To take this into consideration, it isessential that the wafer regions which must be handled are preciselydefined in terms of height and in each rotation position of the wafer.To attain this, a circular support base is advantageously realized forthe wafer, which is as close as possible to the support lines or imagingzones 40, 41. As shown in FIG. 9 b, for this purpose a support plate 50is utilized which has a circular support means 51 with a diameterapproximating very closely the diameter of the position of the imagingzones 40, 41. When the support configuration, which carries the wafer,is rotated for the orientation 52, the handling system is still capableof lifting the wafer after the orientation. A single circular baseconfiguration 51 is especially well suited if cylindrical deformationsof the wafer occur. Similar results can be attained if the wafer isborne by a radially disposed base configuration 53 on the carrier plate50 for staying the wafer as is depicted in FIG. 9 a. This configurationcan be utilized with advantage if the workpiece overall is notcylindrically bent.

In some vacuum process facilities for working semiconductor wafers twoor more robot systems are employed in order to handle the workpieces andto transport them. An important configuration is for example that inwhich a first robot 60 is positioned on a facility at atmosphericpressure at the so-called front end, as it is referred to in thesemiconductor industry, whereby wafers are transported in and out incassettes. The second robot 61 can then be positioned in the vacuumprocess facility, thus under vacuum conditions, in order to transportwafers into the process station and out of the process station. Totransport wafers from atmospheric pressure through a lock into a vacuumand back and subsequently wafers from robot 60 to robot 61 locatedwithin the vacuum chamber, a substrate transfer station 62 is placedbetween the two robots 60, 61. If this substrate transfer station is notlocated on the connection line between the two robot rotation centers66, 67, the wafers 7 placed by the first robot system onto the position63 do not have the correct angular orientation with respect to thesecond robot system at which position 64 would be necessary as is shownin FIGS. 10 a and 10 b. In this case the substrate transfer station 62must be provided with means 65 which permit rotating the wafer about theangular difference between the two required wafer positions 63, 64.

1. Transport mechanism for disk-shaped workpieces (2, 3, 4, 5, 7), inparticular for semiconductor wafers, with a controlled, horizontallymovable transport arm at whose one end two spaced-apart, elongatedcarrying elements (26, 27) are disposed for the substantially horizontalreception of the workpiece and that a cassette (20) is provided, whichat two opposite sides includes a comb structure (18) for thesubstantially horizontal reception of several workpieces (7), thecarrying elements (26, 27) and the comb structure (18) being implementedsuch that these elements can be introduced between two adjacent,spaced-apart combs (19) of the comb structure (18) free of contact withthe workpieces potentially deposited therein, for lifting or depositinga workpiece (7) with the aid of an additional vertical movement relativewith respect to the cassette (20) and the transport arm, characterizedin that the carrying elements (26, 27) are disposed such that during thecassette engagement these are essentially each positioned (18) adjacentparallel to the comb structure along a comb and that in this regionalong and between two adjacent comb planes on one side of the cassette(20) a scanning beam (35) is provided for detecting a workpiece (7) andits position and that the scanning beam (35) is height-positionablerelative with respect to the cassette (20), the scanning beam (35) beingguided tilted by a small angle (34) with respect to the horizontalworkpiece plane.
 2. Transport mechanism as claimed in claim 1,characterized in that for the transport mechanism with transport arm andcassette (20) are defined handling zones (12, 13) within which thecarrying elements (26, 27) interact with the surface of the workpiece(7), wherein these elements with respect to the workpiece are determinedas two spaced-apart parallel opposing strip-shaped areas, which areoriented substantially parallel to the comb structure (18) when theworkpiece is inserted into the cassette (20).
 3. Transport mechanism asclaimed in claim 2, characterized in that the width (11) of the handlingzones (12, 13) is determined by the sum of the vertical systemtolerances (8) of the transport mechanism in combination with themaximal upward and downward bending attained by the workpiece whensupported on a line-form support (1) with its bending angles (9, 10) andwhere these angles intersect with the horizontal planes of the maximumvertical system tolerances.
 4. Transport mechanism as claimed in claim2, characterized in that the workpiece (7) is a semiconductor wafer andthe width of the handling zones is 10 to 20 mm.
 5. Transport mechanismas claimed in claim 1, characterized in that the angle of tilt (34) ofthe scanning beam (35) is defined such that the beam guided along twoadjacent parallel combs (18) the comb distance (19) is not exceeded. 6.Transport mechanism as claimed in claim 1, characterized in that for thepositioning of a workpiece (7) with respect to the cassette (20) amechanism is provided for the vertical movement of the cassette (20). 7.Transport mechanism as claimed in claim 1, characterized in that at theone end of the horizontally disposed comb structure (18) at least onestop means (16, 17) is provided for delimiting the end position of theworkpiece in the cassette (20), this stop means being disposed outsideof the optical path of the scanning beam (35).
 8. Transport mechanism asclaimed in claim 1, characterized in that the carrying elements (26, 27)are implemented in the form of rods.
 9. Transport mechanism as claimedin claim 1, characterized in that a second permissible handling zonewidth (24, 25) is determined, which is smaller than the width of thefirst handling zone (12, 13) and which is located within this firsthandling zone determined by the system tolerances, and that this secondhandling zone width (24, 25) is determined by the cross sectiondimension (21) of the carrying elements (26, 27) and of the cassette gapwidth (23) still free at maximally possible resulting deflections of theworkpiece (7).
 10. Transport mechanism as claimed in claim 1,characterized in that a further, tilted scanning beam (35′) is providedon the opposite side of the first scanning beam (35) in the proximity ofthe opposing other comb structure (18) of the cassette (20). 11.Transport mechanism as claimed in claim 1, characterized in that itcomprises at least two transport robots rotatable about the axes (66,67) with one transport arm (60, 61) each and a rotating mechanism (62)for orienting (65) the handling zones (12, 13) with respect to thetransport direction of the transport arms (60, 61) if the transferposition of the workpiece does not lie on the line connecting the twoaxes (66, 67) of the transport robots.